If Deng Xiaoping can have Socialism with Chinese Characteristics, I can have a Chinese saying with neuroscientific characteristics — “The axon and the dendrite are long and the nucleus is far away” mimicking “The mountains are high and the Emperor is far away”. The professionally offended will react to the latest offense du jour — cultural appropriation — of course. But I’m entitled and I spoke to my Chinese daughter in law, and people over there found it flattering and admiring of Chinese culture that the girl in Utah wore a Chinese cheongsam dress to her prom.
Back to the quote. “The axon and the dendrite are long and the nucleus is far away”. Well, neuronal ends are far away from the cell body — the best example are axons from the sacral spinal cord which in an NBA player can be a yard long. But forget that, lets talk about the ends of dendrites which are much closer to the cell body than that.
Presumably neurons have different types of dendrites so they can respond to different types of inputs. Why should dendrites respond identically if their inputs are different? They don’t. A dendrite responding to acetyl choline will express neurotransmitter receptors distinct from another dendrite on the same neuron distinct from a dendrite responding to dopamine. The protein cohorts of axons and dendrites are different. How does this come about? Because the untranslated part of mRNA on the 3′ end (3’UTR) contains a sequence called a zipcode which binds to specific proteins which then move the mRNA to a specific location in the neuron (axon or dendrite). Presumably all dendrites initially had the same complement of mRNA.
So depending on what’s happening at a particular dendrite on a neuron, more or less of a given protein is made. This is way too abstract. Suppose you want to strengthen a synapse. You’d make more of a neurotransmitter receptor or an ion channel for whatever transmitter that dendrite is getting.
It is well established that axons and dendrites store mRNAs and make proteins from them far from the nucleus (aka the emperor). If you think about it, just how a receptor for dopamine gets to a dendrite receiving dopamine and not to a dendrite (on the same neuron) getting glutamic acid as a transmitter, is far from clear. There are zipcodes distinguishing axons from dendrites, but I’m unaware that there are zipcodes for dopamine dendrites distinct from other types of dendrites.
If that weren’t enough consider [ Neuron vol. 98 pp. 495 – 511 ’18 ]. Even for an mRNA coding for the same protein (presumably transcribed from just one gene), there can be more than one type of 3’UTR (and this in the same cell). Note also that 3’UTRs are longer in neurons than in other tissues.
So the authors looked at the mRNAs in dendrites — they did this by choosing a tissue (the hippocampus) where rows of cell bodies are well separated from their dendrites. They found that for a given dendritic mRNA there was more than one 3’UTR, and that the mRNAs with longer 3’UTRs had longer halflives. Even more exquisitly neuronal activity altered the proportion of the different 3’UTR isoforms. The phenomenon is quite general — over 50% of all genes and over 70% of genes enriched in neurons showed multiple 3′ UTRs.
So there is a whole control system built into the dendritic system, and it varies with what is happening locally.
The emperor emits directives (mRNAs) but what happens locally is anyone’s guess
Chemiotics II 